1. Field of the Invention
The invention relates to a television receiver for receiving a television signal having a data signal associated therewith, said data signal representing pages of text and/or graphics.
2. Description of the Related Art
Such television receivers are well known in which the data signal associated with the television signal is a teletext signal. The teletext signal is multiplexed with the television signal by transmitting it during the vertical blanking interval of a standard analog television signal. The television receiver then includes a teletext decoder which is able to acquire the data signals transmitted in the vertical blanking interval, and store and display one or more pages of the information represented by the teletext data signal. Teletext decoders have become increasingly complex in order to offer additional features, such as FASTEXT, TOP, EPG, Favorite Pages etc. and are normally controlled by a microcontroller which, in order to allow the additional features to be selected and displayed, has increasing amounts of software stored in programme memory associated with the microcontroller. As further features are added the re-writing of this software is an increasingly arduous task. In addition, a series of different teletext decoders which differ in the number of features provided, comprise basically the same hardware, that is microcontroller, data acquisition circuit, and display circuits, but have varying amounts of associated memory for storing the received data and differing programme memory to enable either only basic functions to be performed or allowing more complex additional features to be provided.
One of the known problems with the teletext system is the time taken after a request by a viewer to acquire a particular page of information. This arises because the pages are sent serially and there is a cycle time of the order of 30 seconds for all the data to be transmitted. It is, of course, impossible to acquire and store data apart from when the page is transmitted in the cycle. One way of overcoming this disadvantage is to provide a large amount of data storage in the television receiver so that all pages of a cycle may be acquired in the background and, when the user wishes to view a teletext page, it will then already be stored in the memory. This however, does require a large memory particularly when allowance has to be made for rotating pages as well as the normal magazine pages.
A number of schemes have been devised for anticipating which pages a viewer is likely to wish to access and to give priority to the acquisition and storage of those pages. Examples are the FASTEXT system and the TOP system. In these systems, pages are grouped according to the broadcaster's anticipation of which pages are likely to be of interest to a viewer who has accessed a particular page. With the FASTEXT system, the numbers of the pages which are linked to the page currently selected are sent in extension packets or ghost rows of the teletext signal. The microcontroller then decodes these additional page links and instructs the acquisition circuit to acquire those pages. In the TOP system a different approach is adopted in that a special page, called the Table of Pages is transmitted which indicates those pages which are in the transmission cycle and the way in which they are grouped. Thus, when a particular page is selected, the microcontroller will access the Table of Pages and determine from the Table which further pages should be acquired as being likely to be of interest to a viewer who has selected the page in question.
Further, television receivers are known in which the habits of the viewer are monitored and a list of habitually accessed pages is constructed and stored in memory. These pages are then acquired as soon as the receiver is switched on, or when the received channel is changed, as being the pages most likely to be accessed by the viewer. In this case, the habitually accessed or Favorite Pages will be stored in a portion of the memory associated with the teletext decoder. Thus, provided a minimum time elapses between activating the receiver or changing channel and the viewer deciding to attempt to access teletext pages, then those particular pages will already be available when the viewer requests them and it will not be necessary to wait for them to reappear in the transmission cycle before being able to display them.
A number of other services are also being introduced, such as electronic program guide (EPG), and it is becoming increasingly difficult to determine which pages should be acquired by the data acquisition circuit and stored in memory in order to enable the viewer to have the fastest access to the information.